Mazda Repair: 2002 Mazda Protege LX Code P0421 Warm Up Cat, water pump replacement, timing belt replacement

Question
Bought 2002 Mazda Protege LX 2.0 used 07/15/2008 with 91745 miles.  Thought I should go ahead and get timing belt replaced 08/12/2008 at Mazda dealer at 92095 miles.  They also recommended water pump replacement.  Got that also.  Then the service manager came out to tell me the new water pump was making a noise so they would have to order another one and do everything again.  I did not hear or see the car that day.  The next day, when I went to pickup car, they had three bills for me to sign... the original repair order, one for $0.00, and one for $277.00 for replacing the water pump again under warranty which stated that 'customer states noise coming from under hood after timing belt was replaced'.  The car isn't covered by warranty... must be parts warranty.  They wanted me to sign it so they could get reimbursed for second water pump replacement in case they got audited.  That made me wonder about trusting them.  Then on 08/15/2008 at 92160 miles check engine light came on.  Back to Mazda dealer.  Showed code P0421 Warm Up Cat below Effic..  So I did some research about catalytic converters.  What I found that they should never fail unless there is some other problem.  I also read that it takes several driving cycles of city and highway driving for the monitors to run, the code to reset and the Check Engine light to come on... in my case, I got the check engine light 65 miles after timing belt replacement.  COINCIDENCE?  They already lost my trust.  The Mazda dealer wants to replace the converter for $1147.00.  Do you know of anything they might have done to cause this?  I certainly don't want to go back to this Mazda dealer.

Answer
Not my particular area of expertise but, some notes.

Converters do fail, usually after 90k depending on the driving style.  City cars (short hoppers) tend to corrode while highway cars tend to burn out.  Highway driven converters last longer since converters and other exhaust parts can withstand heat more than corrosion.  That said, just because you MIL (malfunction indicator lamp) came on does not mean it's time to condemn a converter.  Historically Mazda converters and exhaust see 130-150k before issues, again this can vary.

I personally don't like dealerships for service however, it must be considered credible that they took it upon themselves to go back in and swap the pump rather than attempt to deliver the car with the noise issue.  It is also understandable that they attempt a warranty collection on the original pump as the labor costs for them double on your job due to the bad part.  Bad parts are possible and ultimately are the suppliers/manufacturers problem not the dealer.  An independent shop would have to eat the labor and the parts swapped so they are a little off base in my opinion having you sign for that work.  I agree it doesn't look good from a customer prospective.

As for the P0421 issue.  Not likely related though coincidental, yes.  Have the system read then reset or reset it yourself by disconnecting the battery negative terminal and depressing the brake pedal for 10 seconds.  If the MIL comes on again within two drive cycles have the code read again.  If it is the same them my first suggestion would be to change the secondary O2 sensor.  They have had internal issues with several and this may be your problem.  Unless the car has seen a hard 90k then I don't think the converter is the problem just yet.

Hope this helps.